The present invention relates to a sturdy blow-molded container made from a minimum of plastic, and more particularly, the present invention relates to a container having integrally formed inwardly extending ribs which enhance container stability and improve container top loading capabilities. The present invention also relates to a method and an apparatus for making a reinforced blow-molded container.
Various household, automotive and other products, such as liquid, granular or gel products, including shampoo, detergents, motor oil, etc., are commonly packaged and sold to consumers in relatively small-sized, plastic, blow-molded containers, or bottles. For example, in excess of two billion one quart/one liter sized blow molded containers for packaging motor oil are sold annually in the United States alone. Because of the volume of the sales, improvements to the packaging of such products is of significant concern to the packaging industry and to consumers, especially those improvements which relate to the cost of the packaging and its structural capabilities relative to existing packaging.
Plastic blow-molded containers can be manufactured in a variety of shapes and sizes from a variety of plastic materials in any number of known blow molding processes. For instance, many containers are made from high density polyethylene (HDPE) in an extrusion blow-molding process. The containers are required to have sufficient rigidity so that they are able to withstand the rigors of filling, stacking, shipping, handling and eventual use by the consumer.
A significant expense incurred in the manufacture of blow molded containers is the plastic required to make the containers. For instance, a typical one quart blow-molded oil container which meets stability requirements may be manufactured from about 51 grams of HDPE. Significant savings can be achieved by reducing the amount of plastic required to make each container. As an example, assume that HDPE is sold at 40 cents/pound (0.09 cents/gram), that a reduction of three grams of plastic per container can be achieved, and that 100 million containers are to be produced for a given year. The reduction of three grams of HDPE per container results in a savings of $27 million for the year.
The degree of container rigidity required for packing and shipping purposes limits the ability of manufacturers to reduce the amount of plastic consumed in the manufacture of containers. This is because filled containers are packed in bulk in cardboard boxes, or plastic wrap, or both and placed on shipping pallets. A bottom row of packed, filled containers may support several upper tiers of filled containers, and potentially, several upper boxes of filled containers. A commercially-satisfactory container must be sufficiently rigid to resist distortion under these top loading conditions.
The rigidity of containers is measured by vertical compression tests and is referred to as top loading capability. For instance, a one quart oil container may require a top loading capability of about 45 to 50 pounds. A reduction in the amount of grams of plastic in the container can result in a decrease in top loading capability, unless design changes are made to offset the inherent loss of strength due to a reduction in the amount of plastic. Thus, for every container configuration, a balance must be achieved between minimizing the amount of plastic for cost saving purposes and providing a sufficient amount of plastic to provide container rigidity.
Ribs have been utilized in containers for reinforcement purposes. For instance, U.S. Pat. Nos. 5,048,977; 4,781,880; and 4,890,757 which all issued to Robbins III, disclose extrusion blow molding containers with alternating ribs and non-self-supporting webs so that the containers are collapsible in a storage condition and self-supporting in an open position. Also, U.S. Pat. Nos. 3,956,441 and 4,170,622 which issued to Uhlig disclose blow-molded containers having interior ribbed surfaces. U.S. Pat. No. 3,114,932 issued to Donnelly; U.S. Pat. No. 4,496,301 issued to Mozer et al.; U.S. Pat. No. 4,869,862 issued to Bryan; U.S. Pat. No. 5,057,267 issued to Seizert et al.; U.S. Pat. No. 5,198,161 issued to Ogura et al.; U.S. Pat. No. 5,330,342 issued to Linss et al.; U.S. Pat. No. 5,486,333 issued to Mavridis et al.; and U.S. Pat. No. 5,620,722 issued to Spina disclose various methods and apparatus for extruding substantially tubular parisons which have walls with non-uniform thicknesses and which are intended for blow molding.
Although the above referenced ribbed containers may function satisfactorily for their intended purposes, there is a need for a novel blow-molded plastic container which has an exterior configuration similar, or identical, to that which consumers have favored, but which is capable of being manufactured from a reduced amount of plastic while having the same or increased top loading capability. Preferably, the container should be produced according to a novel extrusion blow molding process by apparatus having an extrusion head with a unique configuration that forms longitudinal integral reinforcing ribs on the interior of the container.
With the foregoing in mind, a primary object of the present invention is to provide a blow-molded plastic container which has an exterior surface configuration substantially identical to currently favored containers but which has a reinforced inner surface providing a desirable top loading capability.
Another object of the present invention is to provide a container which provides a sufficient amount of top loading capability while affording a reduction in the amount of plastic used to manufacture the container as compared with known like-sized plastic containers.
A further object of the present invention is to provide a novel method of manufacturing a container having an inner surface with integral longitudinal reinforcement ribs.
A still further object of the present invention is to provide apparatus which is capable of extruding a longitudinally, internally, ribbed parison and which has a uniquely configured extrusion head.
More specifically, the present invention provides a plastic blow molded container having an inner surface with integrally-formed, longitudinally-extending, inwardly-projecting ribs. At least some of the ribs extend continuously from the container finish, vertically along the container sidewall, and into the container base. Preferably, at least some of the ribs extend continuously throughout the entire distance of the container from the top edge of the finish to a central mold parting location on the base. The ribs, which are not visually perceptible when viewing the exterior surface of the filled container, permit the container to be made from a reduced amount of plastic while providing the required amount, or better, of top loading capability.
According to another aspect of the present invention, a novel method of manufacturing a container is disclosed. In it, a substantially tubular parison having an inner peripheral wall with a plurality of spaced-apart, inwardly-projecting, solid ribs is extruded and then positioned within a blow mold. The parison is expanded under pressure into the walls of the blow mold thereby forming a container. The ribs of the parison become ribs on the inner surface of the container and provide a longitudinal reinforcement function, primarily in the sidewalls of the container.
According to yet another aspect of the present invention, apparatus for making the reinforced containers is disclosed. The apparatus utilizes a unique star-shaped mandrel which cooperates with a tubular orifice to permit a substantially tubular parison to be extruded with continuous, longitudinally-extending ribs on an inner peripheral surface of the parison.